With advancement of electronic techniques, portable electronic apparatuses, such as cellular phones, portable personal computers, personal data assistances (PDAs) and portable game machines, have been spread rapidly. Accordingly, electricity storage devices, such as secondary batteries, are in an increasing demand as power supplies for the portable electronic apparatuses. In order to increase the energy densities of the electricity storage devices, research and development for a new electrode active material is being carried out actively.
For example, as a candidate for the new electrode active material, an organic compound capable of causing reversibly an oxidation-reduction reaction is proposed. The organic compound has a specific gravity of about, for example, 1 g/cm3, which is smaller than that of an inorganic oxide, such as lithium cobalt oxide, that has been conventionally used as an electrode active material. Thus, use of the organic compound as an electrode active material may make it possible to develop an electricity storage device having a high energy density. Moreover, it can mitigate risks, such as exhaustion of rare metal resources, resultant soaring prices of the resources, and environmental pollution due to leakage of heavy metal, because the organic compound contains no heavy metal.
As an example of the organic compound that can be used as an electrode active material, a quinone organic compound is known (Patent Literatures 1 to 3, for example). Generally, the quinone organic compound refers to an aromatic compound in which two ketone groups (C═O) are introduced in one aromatic ring.
Patent Literature 1 describes an aqueous secondary battery in which a paraquinone compound and an orthoquinone compound are used as electrode active materials. The paraquinone compound is an organic compound in which two ketone groups are introduced in the para position on an aromatic ring. The orthoquinone compound is an organic compound in which two ketone groups are introduced in the ortho position on an aromatic ring. Patent Literature 1 also describes polymers of quinone organic compounds.
On the other hand, Patent Literatures 4 and 5 each describe a non-aqueous lithium secondary battery in which a quinone organic compound is used as an electrode active material. Patent Literature 5 describes a quinone organic compound (pyrene-4,5,9,10-tetraone) in which four ketone groups are introduced in a pyrene ring.
In this description, a compound having four ketone groups in one molecule is referred to as a “tetraketone compound”. Particularly, a compound having a pyrene ring and four ketone groups introduced in the pyrene ring is referred to as an “aromatic tetraketone compound”.